Russian president Vladimir Putin has called for an end to fighting between Armenia and Azerbaijan over the breakaway province of Nagorno-Karabakh, while the OSCE Minsk Group is meeting in Vienna early next week to discuss the escalations.
European foreign policy chief Federica Mogherini also called for an immediate end to the fighting on Saturday.
Officials from both Armenia and Azerbaijan are blaming the other for violating an Easter truce, and both sides are claiming casualties. Television pictures show a burned out vehicle and craters following shelling overnight.
While an Armenian Defence Ministry spokesman claims it has downed an Azerbaijani helicopter, Azerbaijan is denying this. Azerbaijan also claims to have hit Armenian positions.
"The OSCE Co-Chairs will meet in Vienna on Monday and convene the Minsk Group on Tuesday to address violence in Nagorno-Karabakh," James Warlick, the group's American co-chair, said on Saturday.
'The Co-Chairs call upon the sides to stop shooting and take all necessary measures to stabilize the situation on the ground. They reiterate that there is no alternative to a peaceful negotiated solution of the conflict and that war is not an option," said Warlick and the other two co-chairs, Igor Popov of Russia and Pierre Andrieu of France, in a statement.
Putin has asked both sides to immediately cease fire, his spokesman Dmitri Peskov said at a news conference in Moscow on Saturday. Russia has close relations with both Armenia and Azerbaijan, and sells weapons to both.
Foreign ministers from both countries spoke with Russian foreign minister Sergei Lavrov by phone.